1. Field of the Invention
The present invention relates to a lens, a camera body and a camera system. The present invention is particularly suitable for optical apparatuses, such as film cameras, video cameras and digital cameras, provided with a blur correction function (or vibration prevention function) with which image blur caused by hand vibration of the photographer can be corrected.
2. Related Background Art
Heretofore, many image pickup apparatuses, such as video cameras and film cameras, provided with a blur correction function for preventing deterioration of picked up images (i.e. image blur) caused by hand vibration of the photographer upon shooting have been offered in the market.
The blur correction function used in these image pickup apparatuses is roughly classified into a so-called electrical blur correction system and an optical blur correction system. In the electrical blur correction system, an image signal generated by an image pickup element such as a CCD is picked up, and the image area to be displayed is changed in accordance with the vibration of the camera to display an image without blur. In the optical blur correction system, vibration is detected by a sensor such as a vibration gyro, and the apex angle of a variable apex-angle prism is changed or a part of the image pickup lens is shifted based on the detection result to prevent blur of the picked up image on the image pickup surface.
Here, the outline of both the blur correction systems will be briefly described. In the electrical blur correction system, an image signal output from the image pickup optical system is electrically processed, and then the image signal is temporarily stored in a field memory. After that, the image signal of the current field output from the image pickup optical system is compared with the image signal of the preceding field stored in the field memory to determine the vibration amount, and the image read-out position is shifted as needed to correct the blur of the image. This electrical blur correction system is widely used as a vibration correction system mainly for motion image in video cameras of the like.
On the other hand, in the optical blur correction system, an angular velocity sensor for detecting vibration is provided in the body of the image pickup apparatus, and the optical axis is shifted by means of an optical axis correcting portion such as a variable prism provided in the optical path of the image pickup optical system based on an angular velocity signal obtained from the angular velocity sensor to correct vibration (or blur) of the image on the imaging surface. This system does not suffer from deterioration in picked up images involved by the correcting operation. In addition, since the optical axis angle can be corrected in accordance with the vibration angle of the camera body irrespective of the focal length, image blur can be eliminated excellently even in the case that an image pickup optical system with a long focal length is used. Thus, in terms of image quality, this system is superior to the above system. This optical blur correction system is widely used mainly for correcting image vibration in obtaining still images in film cameras or the like.
As described above, the image blur correction method used in image pickup apparatuses includes the electrical blur correction system and the optical blur correction system, each of which has advantages and disadvantages.
In the electrical blur correction system, blur correction can be achieved easily, but since a portion of image information once stored is used, resolution is deteriorated, and deterioration in image quality is sensible especially when an image of an object in which the image signal includes a large amount of high frequency components, as is the case with, for example, a fine pattern or far landscape is to be picked up.
On the other hand, in the optical blur correction system, although an excellent image can be obtained, it suffers from the problems that a gyro sensor and other parts requires a significant time for activation, and that a significant power is consumed for driving the gyro sensor and other parts. In the digital camera, a kind of the image pickup apparatus, while an object image is to be observed, it is necessary to display a motion picture on a monitor as needed in a manner similar to a video camera, while upon photographing, it is necessary to record a still image with a high image quality as with a film camera.
In view of the above situation, in some prior arts, as disclosed for example in Japanese Patent Application Laid-Open No. 2001-203930, in the recording of an object image, the blur of the object image is optically corrected using an optical blur correction system, and while an object image is displayed on display means without being recorded, the blur of the object image is corrected not optically but by image signal processing by an electrical blur correction system. Thus, power consumption in correcting the blur of the object image is made small while the image is observed before photographing, and the object image can be recorded with a high image quality when photographed.
In the technology disclosed in the above-mentioned document, when the blur correction by image signal processing (or the electrical blur correction) is switched to the blur correction by optical means (or the optical blur correction) while an image is displayed on the display means during the image pickup preparation stage, the optical blur correction means is activated after the operation of the electrical blur correction means is stopped. In addition, when the blur correction by optical means (or the optical blur correction) is switched back to the blur correction by image signal processing (or the electrical blur correction) during the image pickup preparation stage, the electrical blur correction means is activated after the operation of the optical blur correction means is stopped. Accordingly, skipping of the object image occurs upon the switching of the blur correction means, which can cause a trouble in the framing operation upon photographing.